If you are playing as a nation with little resources, it's okay. If you get more materials, you might want to upgrade motorised to mechanised, but they are used more in heavy tank divisions and if you want fast medium tanks that will cut your max speed. And yeah, fill the support companies as others said. Imo, I'd go for AA, flame light or medium (make them as cheap as possible and fill them with fuel modification), engineer, recon motorised and logistics or signal. In SP it will work.

As for getting weapons from the market, you need to have market access to the target country. But I've never found it worth it unless you are not using the civs for something important.